The U.S. Pat. No. 7,741,327 B2 disclosed various synthetic approaches to the aminopyrazole derivatives of formula (I).
However, it was found that the key intermediate 1-nitropyrazole is a high energy compound and was potentially explosive under reaction conditions. In addition, the overall yield of the above mentioned synthetic approaches were low to moderate based on low yielding reaction steps, formation of several by-products, unselective reactions and incomplete conversions.
One object of the invention therefore is to find an alternative synthetic approach which can be applied on a technical scale and which allows to obtain the product in a higher yield and desired purity and without the need of using unsafe intermediates.
The object could be achieved with the process of the present invention as outlined below.